The present invention relates to a controller of a motor, and particularly relates to a motor controller that is able to continue suitable driving even when an open phase failure occurs and no current runs in one of three or more phases of a polyphase motor.
An AC motor in which coils of multiple phases of stators are connected to an inverter is called brushless motor. Such brushless motors are widely used on account of smallness, low power consumption, and long life as compared to brushed motors. A typical example of the brushless motors is a polyphase motor in which coils of three or more phases are connected in star connection. An inverter connected to a DC power source is controlled in accordance with a target torque, and an alternate current is supplied to the coil of each phase.
A polyphase motor of this type, which is used for applications requiring high reliability such as airplanes, is required to continue driving even when an open phase failure occurs and no current flows in one of the phases on account of reasons such as a disconnection in the motor or the inverter. In response to such a request, motor controllers each of which allows the motor to continue driving even if one of phases becomes open have been proposed (see, e.g., Patent Literature 1 (Japanese Unexamined Patent Publication No. H06-280587), Patent Literature 2 (Japanese Unexamined Patent Publication No. 2012-222881), Patent Literature 3 (Japanese PCT application entering national phase in Japan No. WO2005/091488, and Patent Literature 4 (Japanese Unexamined Patent Publication No. 2007-99066)).
The motor controller recited in Patent Literature 1 includes: switching elements provided between a stator neutral point and a cathode of a DC input terminal of an inverter and between a stator neutral point and an anode of the DC input terminal; a current detector configured to detect a current of each coil; an open phase detector configured to perform open phase detection based on a signal from the current detector; and a switching pattern storage configured to store a switching pattern of each of the above-described switching elements and each of switching elements in the inverter, in accordance with an open phase in each phase. When open phase is detected, the switching pattern corresponding to the phase which is open is fetched and the switching of each switching element is controlled.
The motor controller recited in Patent Literature 2 includes: a neutral line connecting a neutral point of a power source with a neutral point of a star connection; a failure detector configured to detect a failure in a coil of each phase; and a failed phase determination unit configured to determine whether a failure has occurred in each phase, based on an output from the failure detector. The motor controller changes the phase of each current in such a way that the locus of the vector of a synthetic current, which is formed by resolving the current of each phase which is determined as not having a failure by the failed phase determination unit into a component orthogonal to the X axis and a component orthogonal to the Y axis and then synthesizing these components, is substantial circular.
The motor controller recited in Patent Literature 3 includes: a current controlling unit configured to determine a multiphase voltage instruction in accordance with a target q-axis current which is equivalent to a target torque, a detected current of each phase, and a motor rotational angle; a normal current controlling unit which is used in a normal state without open phase, and an abnormal current controlling unit which is used in an abnormal state with open phase. One of these controlling units is selected by a switching unit, and the switching elements of the inverter are driven by performing pulse width modulation of the multiphase voltage instruction from the current controlling unit, so that a current is supplied from the inverter to each phase. The abnormal current controlling unit includes: a target phase current shaping unit configured to output, as a multiphase target current, a target current of each phase in accordance with a target q-axis current and a motor rotational angle so that an equilibrium condition in which the sum of the target currents of the respective phases other than the open phase is zero is satisfied; a two-phase transformer configured to perform two-phase transformation of the multiphase target current in accordance with the motor rotational angle, so as to generate a shaped d-axis target current and a shaped q-axis target current; and a dq controlling unit configured to perform dq control based on the shaped d-axis target current, the shaped q-axis target current, the detected current of each phase, and the motor rotational angle, so as to generate a multiphase voltage instruction. The target phase current shaping unit individually specifies the target current of each phase, and the dq control is executed in such a way that the shaped d-axis target current and the shaped q-axis target current are set as the target signals of the d-axis current and the q-axis current.
The motor controller recited in Patent Literature 4 is arranged such that a neutral point of coils of three phases arranged in star connection are connected to a neutral point driving circuit, and a switching unit which is controlled to be turned off in a phase abnormal state is provided to be in series with the coils of the respective phases. A motor controller of a motor driving circuit with which the coils of the respective phases are connected includes a normal-state control map for dq conversion of induced voltage waveforms of the coils of normal three phases and an abnormal-state control map for dq conversion of induced voltage waveforms of the coils of the remaining two phases at the time of open phase. The dq control is carried out with the normal-state control map in the normal state or with the abnormal-state control map in the abnormal state.